Women who have asymmetrical breasts are more likely to develop breast cancer, a study reveals today. The findings published in the journal Breast Cancer Research were based on the mammograms of 504 women taken 27 years ago. A study of the scans found that the odds of developing breast cancer grew by 1.5 with each 100ml increase in breast asymmetry.

Researchers at the University of Liverpool studied the mammograms of 252 women who did not have breast cancer at the time of the mammography but later developed the disease and compared them with the same number of mammograms of healthy women. The results show that women who went on to develop cancer had a higher breast volume asymmetry than women who did not.

Diane Scutt, of the University of Liverpool, said: "It may well be that if [a woman has] a high degree of breast asymmetry then we need to keep a closer eye. But we need to do further work to confirm this before we can apply it clinically."

Breast cancer is the most deadly form of the disease among women and diagnoses have increased by 15% between 1990 and 2000 in England.

Dr Scutt said that asymmetrical breasts did not on their own indicate problems. "As with any risk factor, it shouldn't be viewed in isolation. We had some women who had quite high asymmetry and did not develop the disease and the reverse was true," she said. Less than 1% of women in her study had perfectly symmetrical breasts.

"Most women have some degree of breast asymmetry," she added.

The study confirmed established risk factors for the disease such as a family history, starting periods young and being tall. But the team also found that each 100ml difference in breast size increased breast cancer risk by 50%.

The team found that left and right breasts were equally susceptible to cancer and that there was no trend in asymmetrical women for either the larger or smaller breast to develop cancer.

This goes against some previous studies which suggest that cancer is more common in the left breast and that left breasts tend to be larger, according to Stephen Duffy, an expert in breast screening with Cancer Research UK.

However, the finding of asymmetry as a risk factor is new, said Professor Duffy. "It's quite intriguing and it's not at all clear what might have caused it. The risk is quite small in comparison with other risk factors such as breast density, so it does not have any immediate implications for prevention or screening."

Maria Leadbeater, a breast cancer nurse with the charity Breast Cancer Care, said that further work was needed on asymmetry. But she said it was important for women to be alert to changes. "If your breasts are normally close in size and you notice them becoming asymmetrical it is important to get this change checked out with your doctor."